This invention relates to armature end-windings, and, more specifically, to the series loop blocks and associated tie methods in armature end-windings.
Cooling and ventilation are prime considerations in the design of electric turbomachines. Many of the benefits associated with improved reliability and increased power capability can be traced directly to improved thermal design. In a once-through ventilated hydrogen-cooled generator, the cooling gas from the ventilating fan is distributed into four branches: the gas gap between the rotor and stator, the rotor subslot, the outside space block, and through the end-winding (see FIG. 1). To cool the ends of armature bars near the series loop caps, the cooling gas passes through the gap between the edges of armature bars and the tip of the gas shell. Thus, in order to achieve a relatively uniform temperature distribution and to minimize ventilating windage losses, the cooling flow path must be optimized.
The end-winding support system restrains the movement of the sections of the armature bars that extend outside the core. In the support system, series loop blocks are used to reduce the operational deflections of the series loops at resonance and to withstand electromagnetic forces acting on the series loops. Series loops blocks may be required between every series loop or every other series loop, depending upon the generator type and the vibration characteristics. Two acceptable tie methods for series loop blocking are wrap and frap and X-tie and frap. As an example, a typical view of series loop blocking using X-tie and frap is shown in FIG. 2.
In FIG. 2, reference numeral 40 denotes series loops caps and reference numeral 42 denotes series loop blocks. Since the series loops caps 40 are circularly arranged, the sides of adjacent series loops caps 40 are not parallel to each other. Likewise, the side surfaces of the interposed series loop blocks 42 are not parallel to facilitate a tight fit. Typically, the side surfaces of each series loop block 42 are machined to the extent necessary to obtain a tight fit between the adjacent series loop caps. Alternatively, a build up of felt on the side surfaces of the series loop blocks 42 can be used to obtain a tight fit. In some instances, machining and built up felt is used on the side surfaces of the series loop blocks 42 to obtain a tight fit.
Series loop blocks 42 are conventionally made from solid textolite material, as shown in FIG. 3. Each series loop block 42 is wrapped or tied with resin impregnated felt (not shown). The thickness of the felt is chosen to ensure felt compression of 25% to 50% when the series loop block is installed. However, with installed solid series loop blocks 42, the gas flow path to the outward parts of the series loop caps 40 is blocked, leading to hot spots occurring on these uncooled portions of the winding.
The present invention solves the above described problem by using series loop blocks which support the end-winding bars, improve series loop cooling and increase reliability and efficiency of block bonding. The series loop blocks are machined to include grooves on both sides so as to allow cooling gas to pass through the grooves. This configuration enhances heat transfer and cools series loop caps more efficiently, thereby eliminating hot spots at end-winding series loops.
By providing grooves in the sides of the series loop blocks, the contact areas between the blocks and series loop caps is greatly reduced. The reduction in contact surface area facilitates machining of block contact areas for easier and better fitting of the blocks between series loop caps.
As a consequence, the provision of the grooved series loop blocks increases the operational reliability of generators, by improving the cooling and reducing the vibration of the end-winding series loops. The time to fit and tie the blocks is also reduced resulting in overall winding cycle and cost reductions.